Truelearn Flashcards
How to calculate PAO2 from a given PACO2?
PAO2 = FiO2(PB – PH2O) – PCO2 / RQ
PAO2 = alveolar oxygen partial pressure FiO2 = fraction of inspired oxygen PB = barometric pressure PH2O = vapor pressure of water RQ = respiratory quotient
PAO2 = 0.21 (760 – 47) – PACO2/0.8 ((((((((PAO2 = 150 - PACO2/0.8)))))))
what is the relation between fraction of inspired O2 (FiO2) to pressure inspired oxygen (PiO2)?
PiO2 = FiO2 x (PBar - PH2O).
If PBar and PH2O remain constant, PiO2 and FiO2 are directly proportional.
PiO2 = Pressure of inspired oxygen equation?
PiO2 = FiO2 * (PBar - PH2O)
FiO2 = Fraction of inspired oxygen PBar = Barometric pressure (760 mm Hg at sea level) PH2O = Vapor pressure of water (47 mm Hg at sea level)
What is Fraction of inspired oxygen (FiO2)
is the fraction of oxygen in the volume being measured.
Right shift of O2 dissociation curve causes? (Increased P50)
Acidosis, hypercarbia, hyperthermia, increased 2,3-DPG.
Shift “RIGHT”: (R)ise In 2,3-DP(G), (H+), and (T)emp.
The oxygen affinity for hemoglobin is … (P50 is …) in children than in adults
Lower. and higher P50.
The term P50 is designated as the partial pressure of oxygen (in mm Hg) when oxygen saturation (SaO2) is 50%. In a normal adult, P50 is 27 mm Hg. When the oxyhemoglobin dissociation curve shifts to the left or to the right, P50 will decrease or increase respectively. Thus, P50 can be used to relate the oxygen affinity for hemoglobin.
Why ptn with dependent hypoxia respiratory drive (COPD) May have a PaO2 ~60 without changes in ventilation?
Because the carotid body chemoreceptors sends signals through gloss pharyngeal nerve when PaO2 below 100 but it won’t change ventilation until PaO2 is <60
Pathway of peripheral chemoreceptors hypoxic ventilation drive?
Decrease in PaO2 (not PAO2) will sense the carotid body sinus, fires glossophqryngeal nerve afferent signaling to CNS ventilation centers.
This is inspired by opioids, BZDs, volatiles and b/l carotid endarterectomy
Pathway of central chemoreceptors increasesing reapiration?
They are located in ventral medulla. They sense the increase in H+. (The increase CO2 has the ability to cross BBB (not PaCO2) which then converted to carbonic acid by carbonic anhydride and therefore the increase H increases RR and TV (CO2 -> H2CO3-> H+ -> inc RR and TV).
The systemic met acidosis dose not have the same effect as H+ don’t cross BBB (it’s CO2 that cross BBB)
Factors shifts the CO2 ventilator response curve to left?
Arterial hypoxemia Metabolic academia Surgical stimulation Fear/anxiety Increased ICP
All cause hyperventilating (increases MV with decreasing PaCO2 on curve slope).
Factors shifts CO2 ventilators response curve to right?
Opioids
Barbiturates
Sedatives
Volatiles < 1 MAC
Relationship of pH and PaO2 with Temp
pH inversely to Temp
PaO2 directly to Temp
Direct/indirect hypoxic plum vasoconstrictor inhibitors? (Factors opens up for blood to flow to poorly ventilated lung segment)
Hypocarbia, vasodilator, infection, met alkalosis, gas MAC>1
Indirect associated with increase plum artery pressure; hypervolemia, vasoconstrictor, hypothermia, thrombosis, large hypoxic lung segment
What it effected expiatory/inspiratory loop in intrathoracic obstruction on flow-volume loop?
Intrathoracic obstructions alter the expiratory curve.
(During expiration, intrathoracic pressure becomes positive which further decreases the airway diameter, enhances the degree of obstruction, and impairs airflow.)
What it effected expiatory/inspiratory loop in extrathoracic obstruction on flow-volume loop?
extrathoracic obstructions alter the inspiratory curve.
During inspiration, the negative inspiratory pressure causes the obstruction to increase.
what are causes of plateaued and decreased inspiratory and expiratory on flows-volume loop
A fixed upper airway obstruction or fixed large airway obstruction (e.g., foreign body, tracheal stenosis, large airway tumor) which impairs BOTH inspiration and expiration
The flow-volume loop in a patient with COPD is characterized by …
expiratory phase with a quick peak followed by a much lower than normal plateau phase
Functional residual capacity is the sum of the expiratory reserve volume and residual volume. It is reduced by …
obesity, in females (10% less than males), and when transitioning from upright to supine, prone, or Trendelenburg position.
Interestingly, there is no significant change in FRC as position changes from 0° to Trendelenburg of up to -30°. However, beyond -30°, the drop in FRC is considerable.
A large difference between peak and plateau pressure is suggestive of
If the peak and plateau pressure are not significantly different (normal is 4-10 cm H2O), it suggests an issue with
high airway resistance. Associated conditions such as bronchospasm, kinked endotracheal tube, and mucus plugging should be evaluated and treated.
respiratory compliance such as poor positioning, pulmonary fibrosis, pneumothorax, obesity, or chest wall deformity or compression.
Physiological changes occur with insufflation of abdomen by laprascopic
Decreases lung compliance and increases PIP
Increase V/Q mismatch due to atelectasis and decreases FRC
Elevated CO2 due to CO2 insufflation and decreases lung perfusion and ventilation
PiO2 is the partial pressure of O2 at room air
PAO2 partial pressure of O2 in alveolar equation
PiO2 = (barometric pressure - H2O vapor pressure) x FiO2
PiO2 - (PaCO2/R)
RS system compliance formula?
1/CRS = 1/CL + 1/CCW
Where C is compliance, RS is respiratory system, L is lungs, and CW is chest wall.
Myocardial oxygen supply is affected by …
1) Coronary perfusion:
CBF = (AoDP – LVEDP) / CVR.
2) oxygen content; mainly HR and Hgb
CaO2 = (Hgb * 1.34 * SaO2) + (0.003 * PaO2)
Oxygen dissolved in arterial blood (0.003 x PaO2) raises the total value by only a small amount, therefore its neglected.
Left ventricular systolic pressure affects myocardial oxygen demand or CBF?
myocardial oxygen demand.
has no affect on myocardial O2 supply.
Hypercapnia following administration of oxygen to a patient with COPD is primarily due to …
V/Q mismatching, driven by inhibition of hypoxic pulmonary vasoconstriction. Not due to hypoventilation.
In patients with COPD, hypoxic pulmonary vasoconstriction is the most efficient way to alter the V/Q ratios to improve gas exchange. This physiological mechanism is counteracted by oxygen therapy and accounts for the largest increase of oxygen-induced hypercapnia. A titrated oxygen therapy to achieve saturations of 88% to 92% is recommended in patients with an acute exacerbation of COPD to avoid hypoxemia and reduce the risk of oxygen-induced hypercapnia.
bottom line when increasing FiO2 in COPD patients who have high hypoxic pulmonary vasoconstriction will counteract the vasoconstriction mechanism and steal blood from well-ventilated alveoli.
Main phases of Diastole?
Diastole begins when systole ends and it can be broken into two main phases – isovolumetric relaxation and filling. These main phases can be further broken down into four smaller phases - isovolumic relaxation, rapid inflow, diastasis, and atrial systole.
The main 2 phases of Systole are …
Systole is the ventricular contraction portion, it can be divided into isovolumic contraction and ejection.
Increased Lusitropy on cardiac cycle loop will show?
Positive lusitropy indicates an increase in myocardial relaxation, which allows for a larger end-diastolic volume at a lower end-diastolic pressure. This relationship is illustrated on a cardiac pressure-volume loop by a downward and rightward shift at the end of diastole.
FRC will go down with …
increased weight, decreased height, and in females compared with males.
Also be seen in lung disease such as idiopathic fibrosis, pneumoconiosis, and different forms of granulomatosis and vasculitis.
Following a lung resection a reduction in FRC will be seen; occasionally the remaining lung will expand to fill in some of the space left.
FRC increases with
1) Age because of loss of elastic lung tissue, which lessens the contractile force of the lung and moves the balancing point between the outward force of the chest wall and the inward force of the lung to higher lung volume.
2) COPD, FRC increases faster over the years than in normal subjects because of an effect of chronic air trapping and more severe loss of elastic tissue (in particular in emphysema).
3) increased height secondary to the larger lungs compared to short counterparts.
The R wave signifies the beginning of …
left-ventricular systole, where the mitral valve closes and left ventricle (LV) isovolumetric contraction begins.
End of T wave repolarization signifies the …
Aortic valve closes and LV isovolumetric relaxation begins.
… is defined as the volume of air left in the lungs at the end of breathing, during tidal volume breathing.
Functional residual capacity
FRC = …
FRC = Residual Volume + Expiratory reserve volume
Or
FRC = Total lung capacity – Inspiratory capacity
… is the volume of air in the lungs below which airways begin to collapse
Closing capacity
… is the amount of air that can be actively exhaled at the end of a tidal volume breath.
The expiratory reserve volume
… is the amount of air left in the lungs at the expiratory reserve volume.
Residual volume
… is the amount of air that is moved with a maximal inhalation and forced exhalation.
Vital capacity
